docs: def _weeks_check(self, data, week_type):
          """Check if input for the typical/extreme weeks of the header is correct."""
          assert isinstance(data, dict), '{}' \
              ' must be an OrderedDict. Got {}.'.format(week_type, type(data))
          if bool(data) is True:
              for val in data.values():
                  assert isinstance(val, AnalysisPeriod), '{} dictionary must contain' \
                      ' AnalysisPeriod objects. Got {}.'.format(week_type, type(val))
                  assert len(val.doys_int) == 7, '{} AnalysisPeriod must be for'\
                      ' a week.  Got AnalysisPeriod for {} days.'.format(
                          week_type, type(val))